Optical disk apparatus compatible with different types of mediums

Abstract

A polarizing beam splitter for separating an upstream beam from a downstream beam according to the polarization of an incident beam is provided between first and second light sources emitting laser beams at respective wavelength and an objective lens. A phase plate for providing a phase difference to a beam incident on the polarizing beam splitter is provided between the polarizing beam splitter and the light sources. A portion of the laser beam incident on the polarizing beam splitter is reflected by the polarizing beam splitter and caused to be incident on a photo-detecting unit, so as to prevent an unnecessary portion of the laser beam is incident on the photo-detecting unit. According to the invention, the laser beam is used efficiently and the cost of fabricating an optical disk apparatus is reduced by eliminating a need for a gain controlling circuit in the photo-detecting unit.

What is claimed is:  
     
       1. An optical pickup apparatus compatible with a first optical recording medium adapted for a first wavelength for writing and reading and a second optical recording medium adapted for a second wavelength for writing and reading, comprising: 
       a first light source emitting a first beam at the first wavelength;  
       a second light source emitting a second beam at the second wavelength;  
       a coupling lens for coupling one of the first beam and the second beam;  
       an objective lens for converging the coupled beam so as to form a beam spot on a recording surface of one of the first optical recording medium and the second optical recording medium;  
       optical path separating means for separating a return beam reflected by the optical recording medium and transmitted through the objective lens, from an upstream optical path leading from the light source to the objective lens, said optical path separating means being provided in alignment with both an upstream beam traveling to the recording surface and the return beam;  
       detecting means for receiving the return beam separated by said optical path separating means so as to retrieve information from the return beam, said detecting means being provided in alignment with both the upstream beam and the return beam and including photosensitive means;  
       control means for effecting focusing control and tracking control based on a result of detection by said detecting means, wherein  
       said first light source is driven only when the first optical recording medium is used, the second light source is driven only when the second optical recording medium is used,  
       said coupling lens is an anamorphic lens and is provided with a collimating function for collimating one of the first beam and the second beam and a beam shaping function for shaping one of the first beam and the second beam; and  
       optical axis aligning means for aligning optical axes of the first beam and the second beam with an optical axis of said coupling lens, wherein said optical axis aligning means is embodied by a combination of a prism element having one of a variable transmissivity and a variable reflectivity that depends on a polarization of an incident beam, and a phase plate for rotating a plane of polarization of one of the first beam and the second beam by 90°.